Question 1132100
<pre>
(1)  {{{ a + ar + ar^2 = 42 }}} 
(2)  {{{ ar^3 - a = 42 }}}  <br>

</pre>
So we have {{{  a + ar + ar^2 = ar^3 - a }}}
{{{ 1 + r + r^2 = r^3 - 1 }}} 
{{{ 1 + r + r^2 = (r - 1)(r^2 + r + 1) }}}
{{{  1 = (r - 1) }}}<br>

Common ratio:
{{{ highlight( r = 2 ) }}}<br>

First term:
from (1):  {{{ a + 2a + 4a = 42 }}} --> a = 6
             
{{{  highlight( a = 6 ) }}}
<br>
Check:
6 + (2)(6) + (4)(6) = 6 + 12 + 24 = 42 (ok)
8(6) - 6 = 48 - 6 = 42  (ok)